openstack/devstack
Code Issues Proposed changes

Enable direct-io on LVM loop devices

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This enables direct-io on the loop devices that we create for LVM backing
stores. The goal here is to reduce the buffer cache overhead involved with
loop mounting a very large file on a filesystem, as well as potentially
providing a little more block-device-like behavior for things that expect
them. We are hoping this will address some of the very long LVM calls that
cinder does, which randomly take a very long time, causing timeouts.

The loop direct-io support was added in kernel 4.4.0, which was xenial,
but the losetup binary does not have the required flag. Thus, this patch
checks the "losetup -h" output for the flag before deciding to enable it.

Change-Id: Idc69cf3598d6ed6646c0145733c90ad0b1b60883
This commit is contained in:
Dan Smith 2018-12-14 06:39:59 -08:00 committed by Ian Wienand
parent 8fc227f63f
commit 93a94f503b
1 changed files with 8 additions and 1 deletions
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9
lib/lvm
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@ -99,8 +99,15 @@ function _create_lvm_volume_group {
if ! sudo vgs $vg; then
# Only create if the file doesn't already exists
[[ -f $backing_file ]] || truncate -s $size $backing_file
local directio=""
# Check to see if we can do direct-io
if losetup -h | grep -q direct-io; then
directio="--direct-io=on"
fi
local vg_dev
vg_dev=`sudo losetup -f --show $backing_file`
vg_dev=$(sudo losetup -f --show $directio $backing_file)
# Only create volume group if it doesn't already exist
if ! sudo vgs $vg; then